1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display device by an One Drop Fill process, and more specifically, to a method for manufacturing a liquid crystal display device which has two substrates opposed to each other with spacers disposed therebetween to form a fixed gap and which also has a liquid crystal layer disposed between these substrates.
2. Description of the Related Art
As disclosed in Japanese Patent Publication No. H11-326922 for example, an ODF process (One Drop Fill process) has been conventionally used to manufacture liquid crystal display devices. The ODF process disclosed in this patent document will be described as follows. FIG. 1 is a plan view showing a conventional method for manufacturing the liquid crystal display device by the ODF process. In FIG. 1, an active matrix substrate is in the process of being manufactured.
As shown in FIG. 1, first, scan lines, data lines and pixel circuits (not shown) including TFTs (Thin Film Transistors) and the like are formed on a surface of a glass substrate 101 to prepare an active matrix substrate 110. Then, rectangular frame-like sealing members 102 and 103 are formed doubly on the surface of the active matrix substrate 110 that has the pixel circuit thereon. The sealing members 102 and 103 can be made of, e.g. an ultraviolet curable resin. The sealing member 102, which is inside the sealing member 103, is formed so as to surround the display region of the liquid crystal display device. Between the inner sealing member 102 and the outer sealing member 103 is formed of a ring-like region 104. Then, liquid crystal 106 is dropped in a region 105 which is inside the sealing member 102.
On the other hand, a color filter (CF), a black matrix and the like are formed on a surface of another glass substrate to prepare a color filter substrate (not shown). The color filter is provided with a plurality of pillar-like spacers thereon.
Then, in a vacuum, the color filter substrate is superimposed on the active matrix substrate in such a manner that the surface of the color filter substrate having the color filter thereon can be opposed to the surface of the active matrix substrate on which the liquid crystal 106 has been dropped. Next, the superimposed structure of the color filter substrate and the active matrix substrate is taken out to the atmosphere. As a result, the regions 104 and 105 are sealed air-tight, thereby being made a negative pressure. In particular, the region 104 not filled with the liquid crystal 106 is evacuated, so that the atmospheric pressure applied on the region 104 causes the active matrix substrate and the color filter substrate to be pressed toward each other. On the other hand, the spacers formed on the color filter substrate prevent the distance (hereinafter, the gap) between the active matrix substrate and the color filter substrate from becoming less than a specified value. This results in the formation of a uniform-thick liquid crystal layer between the active matrix substrate and the color filter substrate.
Next, the sealing members 102 and 103 are hardened by being exposed to ultraviolet radiation. This enables the active matrix substrate and the color filter substrate to be laminated to each other. Then, the active matrix substrate and the color filter substrate are cut along cutting lines 107 set along the sealing member 102 on the region 104. As a result, the region including the sealing member 103 is cut off to form a liquid crystal display device.
Also, Japanese Patent Publication No. 2001-281678, for example, discloses a technique in which the height of the spacers formed on the color filter substrate is measured, the optimum amount of the liquid crystal 106 to be filled in the region 105 is calculated based on the spacer height, and the dispenser for the liquid crystal 106 is controlled based on this calculated amount. This patent document describes, as its method for controlling the drop amount, selecting the number of drop shots, and preparing two dispensers having different numbers of drops per shot from each other and selecting the dispenser to drop the last shot.
However, the aforementioned conventional techniques have the following problems. In the conventional method for manufacturing the liquid crystal display device shown in FIG. 1, the two sealing members 102 and 103 are formed around the display region. This forces to use of glass substrates much larger than the final products of the active matrix substrate and the color filter substrate, thereby causing a cost increase.
However, in the absence of the sealing member 103, when the superimposed structure of the color filter substrate and the active matrix substrate formed in a vacuum is taken out to the atmosphere, the vacuum region 104 is not formed. Therefore, the active matrix substrate and the color filter substrate are laminated only by the negative pressure of the region 105 filled with the liquid crystal 106. This makes the force to press these substrates inward insufficient, thereby causing the gap between the substrates to be non-uniform. In particular, the gap in the peripheral areas of the region 105 is liable to be non-uniform. A gap larger than the designed value causes images displayed on the liquid crystal display device to be yellowish. In contrast, a gap smaller than the designed value causes the images to be bluish. Thus, a non-uniform gap leads to degradation in display quality.